1. Field of the Invention
The invention relates to the assembly and movement control of an element that can move angularly with respect to a support between two extreme positions.
It concerns in particular, but not exclusively, the assembly and movement control of a shutter adapted to close, or open, an aperture of an optical space instrument, for example, a terrestrial or stellar observation telescope.
2. Description of the Prior Art
As is known, there are certain phases in the life of an optical space system during which its aperture must be closed. This not only applies to the launch of the space vehicle in which this optical space system is mounted until the space vehicle is in its service configuration, but also later in the normal service life of this optical system, in particular when, because of the attitude of the space vehicle, the optical system is subjected to subsequent risk of attack from such things as sun glare, collision with foreign particles, and the like.
The closing and opening of the aperture of such an optical system involves the operation of a shutter panel or flap between an open configuration in which the aperture of the system is open and a closed configuration in which no beam, of light or particles, can enter the optical system.
It should be noted that the function (temporary protection) of the shutter flap considered here differs from that of the shutter of a camera which must be operated at high speed so that it remains open for only a very short exposure time.
It should be also be noted that the fact the shutter flap must be operated in the vicinity of an optical system excludes the use of lubricants, not only because of the surrounding space vacuum, but also because of risks of these lubricants polluting any cold surfaces of the optical system such as, for example, is the case with infrared observations which involve cooling of the optical system itself.
Taking into account that the purpose of the assembly and movement control device, also referred to as "mechanism" hereinafter, is to be on board a space vehicle, no human intervention is possible in the event of failure. Now it may appear necessary, at any time during the life of the space vehicle, to move the shutter from one of its positions to the other, failing which the continuation of the mission may be irretrievably compromised, with economic results that can be imagined. Increasing levels of reliability are, therefore, sought for such a device, particularly since the life expectancy of space vehicles, particularly satellites, is tending to increase; durations of the order of ten years are often sought.
Attempts have already been made to attain high reliability, but in practice by proposing to use electric motors, with ball bearings. This can lead to bonding of parts in contact because of the space vacuum, leading to risk of damage.